The Humboldt Current System (HCS) is one of the most productive marine ecosystems on earth. It extends along the west coast of South America from southern Chile (∼42°S) up to Ecuador and the Galapagos Islands near the equator. The general oceanography of the HCS is characterised by a predominant northward flow of surface waters of subantarctic origin and by strong upwelling of cool nutrient-rich subsurface waters of equatorial origin. Along the coast of northern and central Chile, upwelling is localised and its occurrence changes from being mostly continuous (aseasonal) in northern Chile to a more seasonal pattern in southern-central Chile. Several important upwelling centres along the Chilean coast are interspersed with long stretches of coast without or with sporadic and less intense upwelling. Large-scale climatic phenomena (El Nino Southern Oscillation, ENSO) are superimposed onto this regional pattern, which results in a high spatiotemporal heterogeneity, complicating the prediction of ecological processes along the Chilean coast. This limited predictability becomes particularly critical in light of increasing human activities during the past decades, at present mainly in the form of exploitation of renewable resources (fish, invertebrates and macroalgae). This review examines current knowledge of ecological processes in the HCS of northern and central Chile, with a particular focus on oceanographic factors and the influence of human activities, and further suggests conservation strategies for this high-priority large marine ecosystem. Along the Chilean coast, the injection of nutrients into surface waters through upwelling events results in extremely high primary production. This fuels zooplankton and fish production over extensive areas, which also supports higher trophic levels, including large populations of seabirds and marine mammals. Pelagic fisheries, typically concentrated near main upwelling centres (20-22°S, 32-34°S, 36-38°S), take an important share of the fish production, thereby affecting trophic interactions in the HCS. Interestingly, El Nino (EN) events in northern Chile do not appear to cause a dramatic decline in primary or zooplankton production but rather a shift in species composition, which affects trophic efficiency of and interactions among higher-level consumers. The low oxygen concentrations in subsurface waters of the HCS (oxygen-minimum zone, OMZ) influence predator-prey interactions in the plankton by preventing some species from migrating to deeper waters. The OMZ also has a strong effect on the bathymetric distribution of sublittoral soft-bottom communities along the Chilean coast. The few long-term studies available from sublittoral soft-bottom communities in northern and central Chile suggest that temporal dynamics in abundance and community composition are driven by interannual phenomena (EN and the extent and intensity of the OMZ) rather than by intra-annual (seasonal) patterns. Macrobenthic communities within the OMZ are often dominated in biomass by sulphide-oxidising, mat-forming bacteria. Though the contribution of these microbial communities to the total primary production of the system and their function in structuring OMZ communities is still scarcely known, they presumably play a key role, also in sustaining large populations of economically valuable crustaceans.

The humboldt current system of northern and central chile : Oceanographic processes, ecological interactions and socioeconomic feedback

To investigate the influence of marine macrophyte wrack subsidies on community structure, relationships between community attributes, including species richness, abundance, and biomass of macrofauna and abundance of shorebirds, and a variety of factors, including the standing crop of wrack and beach morphodynamics, were examined on 15 exposed sandy beaches on the southern California coast. The beaches sampled were primarily modally intermediate morphodynamic types, and three were groomed regularly. Species richness, abundance, and biomass of the macrofauna were high compared to values reported for similar beach types in other regions and were not predicted by morphodynamics or other physical factors. Overall species richness and abundance, and the species richness, abundance, and biomass of wrack-associated fauna and selected taxa were significantly correlated with the standing crop of macrophyte wrack. Wrack-associated macrofauna, such as amphipods, isopods, and insects, made up an average of >37% of the species on ungroomed beaches and comprised 25% or more of the total abundance on half of those beaches. The abundance of two shorebird species, plovers that forage using visual cues, was positively correlated with the standing crop of wrack and with the abundance of wrack-associated invertebrates. Significant differences in community structure, including depressed species richness, abundance, and biomass of macrofauna, especially for wrack-associated taxa, were associated with beach grooming and provided strong evidence for the bottom-up effects of wrack subsidies. Grooming also reduced the prey available to vertebrate predators, such as shorebirds. Substantial ecological effects of the large-scale disturbance and removal of organic material, food resources, and habitat are associated with beach grooming. These results suggest that macrophyte wrack subsidies strongly influence macrofaunal community structure, higher trophic levels, and ecological processes on exposed sandy beaches. The supply of macrophyte wrack should be considered as a factor in ecological studies of exposed sandy beaches, particularly where macrophyte production is high.

The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California

Physical and biological factors govern com- munity and population features of sandy beach macro- fauna. At the macroscale, species richness decreases from tropical to temperate beaches, and from macrotidal dissipative to microtidal reflective beaches. At the species level, life history traits are highly plastic over latitudinal gradients; large-scale variations in environmental vari- ables modulate intraspecific phenotypic differentiation. At the mesoscale, alongshore and across-shore distribu- tions tend to be unimodal, bell-shaped within a beach, with abundance varying from the central region to the boundaries, even though environmental gradients (wave exposure, salinity) can cause asymmetries. Zona- tion is highly dynamic and not sharply defined. This is attributed to short- (hourly, daily) or medium- (seasonal) term reactions to environmental conditions, passive transport and sorting by the swash (e.g. recruits), active micro-habitat selection (e.g. adults), and intra- and inter- specific interactions. Across-shore distribution may be- come multimodal due to intraspecific segregation by sizes during recruitment. At the microscale (individual neighbourhood or quadrat scale), behavioural factors and intra-/interspecific interactions become more important as density increases. Human induced impacts also gener- ate variability in population demography, structure and dynamics. We identify physical-biological coupling at dif- ferent temporal and spatial scales, emphasizing the role of life history traits in order to assess alternative regula- tory mechanisms and processes. Our synthesis suggests that: (1) biological interactions are more important regu- latory agents than previously thought: in benign dissipa- tive beaches or undisturbed sites, intra- and interspecific competition can be more intense than in reflective beach- es or disturbed sites, where the populations are physi- cally controlled; (2) supralittoral forms are relatively inde- pendent of the swash regime and show no clear response to beach type; (3) marked long-term fluctuations are noticeable in species with planktonic larvae structured as metapopulations, due to environmental disturbances and stochasticity in reproduction and recruitment.

/pdf/patterns-processes-and-regulatory-mechanisms-in-sandy-beach-2cxtvqdmoi.pdf

Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis

Beach-cast wrack is a prominent feature of beaches of south-western Australia. We examined the fauna of these beaches to explore the generalisation [Polis, G.A., Hurd, S.D., 1995. Extraordinarily high spider densities on islands: flow of energy from the marine to terrestrial food webs and the absence of predation. Ecology 92, 4382–4386] that beach-cast wrack from highly productive marine ecosystems subsidises low productivity of terrestrial ecosystems, to establish whether this generalisation is relevant to oligotrophic marine systems. We sampled three beaches with high and three beaches with low volumes of beach-cast wrack to determine if: (1) the presence of wrack influences the abundance of macroinvertebrates; (2) wrack acts as a food source for beach macroinvertebrates; and (3) the influence of wrack varies between zones above the high water mark. We measured wrack volume and composition, sediment characteristics, the abundance of different epibenthic and infaunal macroinvertebrates taxa, and δ 13 C and δ 15 N of macrophytes and macroinvertebrates. The mean volume of wrack on high-wrack beaches was 0.27–1.07 m 3 wrack m −2 compared to 0.00–0.09 m 3 wrack m −2 on low-wrack beaches. There were no significant differences in sediment grain size, moisture content or loss on ignition between the two types of beaches or zones. Epibenthic fauna and infauna were consistently abundant on high-wrack beaches (20–291 and 0.5–3.5 individuals 0.64 m −2 , respectively), but either absent or extremely rare in low-wrack beaches (0–3 and 0–0.1 individuals 0.64 m −2 , respectively). Within high-wrack beaches, there were no significant differences in the abundance of epifauna or infauna among beaches or between zones. The δ 13 C values of macroinvertebrates at all sites were most similar to red and brown algae, with the exception of beetles from two beaches, which were closest to seagrasses. Mixing model (Isosource) results for mesograzing amphipods and dipteran flies suggested carbon was assimilated mostly from the seagrass Posidonia spp., the dune grass Spinifex longifolia and red algae for amphipods and from brown algae, red algae and dune vegetation for dipteran flies. We conclude that the presence of marine-derived wrack plays a major role in subsidising production of macroinvertebrates on beaches of south-western Australia. We suggest that marine subsidies can play a role in supporting terrestrial production, even in oligotrophic marine environments.

Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat

The humboldt current system of northern and central chile

During two field studies the macrofauna associated with wrack stranded on a tropical sandy shore was analysed. During the first period all animals present in small wrack deposits were randomly collected with cores. During the second field study active animals were sampled in larger wrack deposits for an entire lunar period, and tube traps were used. After a comparison between the two studies, only the data from the tube traps were examined from a temporal and spatial point of view. The aim of the present work was to gain information on how, when and where wrack was colonised by invertebrates, keeping in mind cyclical aspects such as lunar, diel and tidal phases. Predatory taxa, such as Staphylinoidea and the amphipods Talorchestia martensii, were most abundant, whereas Diptera larvae and Tenebrionidae were scarce. Successional changes of beach wrack colonisation were evident throughout a semi-lunar period, with molluscs invading wrack during the first days of deposition and histerids during the last ones. Strictly nocturnal or diurnal surface-active species were found to be active in the wrack during both the day and the night. The analysis of the tidal component of species activity in the wrack showed that some species moved at ebbing tide, and others moved at rising tide. Differences were found also in the mean hours of tidal activity, calculated separately during day and night periods. The study of the zonation of each species showed that in some cases wrack deposits were closely followed by the fauna as their position changed during the semi-lunar phase. In other cases differences occurred between species zonation during day and night periods and tidal phases. Cluster analysis indicates that most species exploit the wrack in different ways (as refuges and/or feeding site), both in space and in time.

Temporal and spatial use of stranded wrack by the macrofauna of a tropical sandy beach

A study on the surface activity and zonation ofTalorchestia britoand of two age classes ofTalitrus saltatorwas done along the French Atlantic coast. Samples were taken with a transect of pitfall traps and climatic data were recorded. The data were collected during two periods of 48 hours, one around spring tide and the other around neap tide. Activity patterns, mean hours of activity, total and hourly mean zonations and hourly orientation indices were calculated in daily and tidal hours at both spring and neap tides. Simple correlation analysis was used to compare between species and within age classes both the trends of the distributions of the activity patterns and those of the hourly mean zonations. Multiple regression analysis was employed to correlate surface activity and hourly mean zonation with environmental factors. The results indicate that both species were nocturnal and that most activity occurred on the ebbing tide. Total mean zonations changed between the two synodic phases with a landward shift at spring tide. Also, the hourly mean zonations varied during the activity period according to the tides and synodic phases. Juveniles ofT. saltatorpresented a more landward distribution compared with adults and compared withT. britowhich was always found closer to the sea. Zonation patterns seem to be related in a complex way to the environmental variables such as air relative humidity, sand temperature and moisture, atmospheric pressure and tidal elevation. Furthermore it was emphasized that for certain aspects the behavioural strategies of adultT. saltatordiffered from those of the juveniles and ofT. brito. On the whole this work shows the behavioural plasticity of littoral talitrids and the different strategies of two sympatric species in the use of space and time.

Differences in Behavioural Strategies between Two Sympatric Talitrids (Amphipoda) Inhabiting an Exposed Sandy Beach of the French Atlantic Coast

Spatial distributions of sand beach arthropods were studied at Zouara (Nefza), a beach dune system along the northwestern coast of Tunisia. Two transects with pitfall traps, perpendicular to the shoreline and placed from sea towards land, captured spontaneously crawling arthropods. The pitfalls were used to obtain data on horizontal zonations for 2  days during different seasons (April, October). In April, in order to assess local, long-shore distributions of surface-active beach invertebrates, ten transects with pitfall traps were placed every 100 m, for 2 days. Core samples were also taken in correspondence with each of the ten transects to obtain the distribution of burrowing individuals. Sand samples were taken for successive laboratory analyses (salinity, grain size and organic contents). Local climatic conditions were also recorded. One isopod (Tylos europaeus, subdivided into three different size classes), two amphipods (Talitrus saltator, Talorchestia brito and indistinguishable juveniles) and four coleopteran species (Eurynebria complanata, Scarites laevigatus, Phytosus nigriventris, Phaleria acuminata) were considered. Mean zonations perpendicular to the shoreline showed that crustaceans were found closer to the sea-line limits than coleopterans and that between seasons some species changed their mean zonation more than others. Local, long-shore distributions of active and burrowing individuals showed that most species were unevenly distributed along the shore. These discontinuous distributions differed according to the species and age class and were mainly related to specific microclimatic conditions and to nutrition.

Small-scale spatial and seasonal differences in the distribution of beach arthropods on the northwestern Tunisian coast. Are species evenly distributed along the shore?

Two sympatric species from an exposed sandy beach in north-western Tunisia, the sandhoppers Talitrus saltator (Montagu) and Talorchestia brito Stebbing, were compared as regards orientation under natural conditions. Sets of experiments were carried out on the beach using two experimental arenas, one permitting the view of both the sky and landscape and the other of the sky only. Replicates were made at different hours of the day, in different days and period of the year and with various climatic conditions. Multiple regression models were fitted to the angular data obtained. These models allow an estimate of the trends of variation depending on a combination of factors. The simultaneous effects of environmental factors influencing orientation were quantified for each species. The sun was confirmed as the major orientation cue in these populations, but the concentration of directional choices was enhanced by the landscape vision. The climatic factors affected orientation in different ways depending on the time of day and year. When the two species were compared, Talitrus saltator showed a higher flexibility of response than Talorchestia brito under the same environmental conditions, supporting the hypothesis of a higher level of terrestrialization of the former species.

https://www.jstor.org/stable/pdfplus/4602069.pdf

Multiple regression analysis of the sources of variation in orientation of two sympatric sandhoppers, Talitrus saltator and Talorchestia brito, from an exposed Mediterranean beach

During the dry season (1971) and the wet season (1973) two field studies were conducted at Sar Uanle, a locality along the coast of Somalia (East Africa). The study analysed the beach–dune system considering ecological aspects in a dynamic way. During the two periods of study and for an entire synodic period, a system of traps (directional pitfall traps) was used. At the same time the climatic factors were registered. For the most abundant arthropod species mean zonations were calculated during surface activity and considered in relation to the season, diel, synodic and tidal phases. The variations in mean zonation were then correlated with the main environmental parameters. During the wet season, for some taxa orientation indices were calculated. The results indicate that two distinct subcommunities are present at Sar Uanle: a more dynamic one on the beach and another on the dune. Arthropod species living in this beach–dune system have evolved behavioural strategies in relation to cyclical environmental changes according to their physiological needs, locomotory capacities and zonation.

A. Aloia

Papers

Temporal and spatial use of stranded wrack by the macrofauna of a tropical sandy beach

Differences in Behavioural Strategies between Two Sympatric Talitrids (Amphipoda) Inhabiting an Exposed Sandy Beach of the French Atlantic Coast

Small-scale spatial and seasonal differences in the distribution of beach arthropods on the northwestern Tunisian coast. Are species evenly distributed along the shore?

Multiple regression analysis of the sources of variation in orientation of two sympatric sandhoppers, Talitrus saltator and Talorchestia brito, from an exposed Mediterranean beach

Spatial Use of an Equatorial Coastal System (East Africa) by an Arthropod Community in Relation to Periodically Varying Environmental Conditions